A study conducted by Brazilian researchers shows how age influences the effectiveness of the two main immunizers used in the country against Covid-19. Submitted as a preprint in MedRxiv (updated version with data disclosed in this article will be available soon), the study Influence of age on effectiveness and duration of protection in the Oxford/AstraZeneca and CoronaVac vaccines involved more than 75 million immunized people, becoming the largest study conducted with the two immunizers and may serve as a basis for guiding public health decisions, including the need for additional doses or booster doses.

Coordinated by Manoel Barral-Netto, researcher of Fiocruz Bahia, the work evaluated the effectivenss of vaccines in 75,919,840 people vaccinated in Brazil between January 18th and July 24th, 2021. Results show that both vaccines are effective against infection, hospitalization, an ddeath, considering the full vaccination scheme (two doses): AstraZeneca/Fiocruz, with 90% of protection, and CoronaVac, with 75%. The research also showed that both vaccines offer protection against moderate and severe cases of Covid-19 regarding the variants of concern circulating in Brazil during the period of analysis.

However, when separating the vaccinated groups by age, the data show that there is a reduction in protection with increasing age and that the two vaccines offer different protection degrees with the full vaccination schedule. From to 89 years old, the AstraZeneca/Fiocruz vaccine had a protection rate against death of 89.9%, while CoronaVac had 67.2%. Over the age of 90, these rates were 65.4% in those vaccinated with AstraZeneca/Fiocruz and 33.6% with CoronaVac. In people between 80 and 89 years old, the AstraZeneca/Fiocruz vaccine offered 89.9% protection against death, while CoronaVac offered 67.2%. For those above 90 years old, these rates remained around 65.4% in those vaccinated with AstraZeneca/Fiocruz and 33.6% with CoronaVac.

“We already suspected that age influenced the drop in effectiveness, because this happens with other vaccines as well. What we did was to delineate this point of decline very clearly. This is also the first comparison made between vaccines that use different platforms", said Barral-Netto. "The intention is to provide data on which to base decisions for managers.

Importance of research in Brazil

AstraZeneca/Fiocruz has already been approved in 181 countries, while CoronaVac has been approved in 39. However, few nations can offer such a large database for a study of this size. Although the 211 million Brazilians are divided in different regions, the system that collects health information is the same for the entire country, providing a huge source of data that allowed for this analysis per age group. For this purpose, the study used data of the National Immunizations Program (PNI), of e-SUS-Notifica, and of the Information System for Influenza Epidemiological Surveillance (Sivep-Gripe).

Source: Fiocruz News Agency (AFN, acronym in portuguese).